(1) Field of the Invention
The present invention relates to a method of identifying a target effective pigment comprising preparing a database of image characteristic parameters of effective pigments of color layers in metallic/pearl coating or printing used to impart specific design effects; and an effective pigment identification system, an effective pigment identification program, and a recording medium therefor.
(2) Description of the Related Art
When an automotive outer panel is subjected to repair coating, the repaired portion needs to have the same color as the other portions of the panel. However, since the formula of the coating used at the time of car manufacturing are not publicly available, analysis of the coating formula may be necessary.
A computer color matching technique (hereinafter referred to as “CCM”) comprising estimating a formula from data obtained by color measurements has been developed and used as a method for analyzing the formula of a coating whose composition is unknown.
CCM is a method for estimating color materials (color pigments, dyes) of a solid coating color (color whose appearance does not change with the angle of observation) from spectral reflectance data. This method uses Kubelka-Munk's two-flux theory, Duncan's color-mixing theory, and Saunderson's surface-reflectance correction theory in combination.
Japanese Unexamined Patent Publication No. 2001-265786 (hereinafter referred to as “Patent Document 1”) discloses a method of identifying an effective material used in a coating color whose formula is unknown, the method comprising: visually extracting a characteristic parameter of the effective material used in a coating color whose formula is unknown; searching through an image database using the extracted characteristic parameter as a keyword; displaying on a monitor an image of a single effective material that most closely matches the parameter; and comparing the image of the coating color whose formula is unknown to the image of that single effective material.
However, no CCM method for coating colors containing effective pigments (e.g., aluminum flakes and like metal powders, mica flakes, plate-like iron oxide, etc.) has yet been developed for practical use for the following reasons. At the highlight portions which include the place where light's specular reflection occurs, the additive property of light beams (specularly reflected light, interference light) reflected from the effective pigment holds, and light absorption by color pigment(s) also occurs. In contrast, at the shadow portions which are not affected by specular reflection light, light absorption by effective pigment(s) and color pigment(s) mainly causes coloring. That is, it is impossible to generalize coloring characteristics of color materials of a coating containing effective pigment(s) over such a wide range as from highlight to shadow portions.
Therefore, a conventional method for identifying an effective pigment in a coating applied to an industrial product comprises observation by the naked eye or with a microscope and identification based on the observer's knowledge of characteristics of effective pigments. Therefore, experience and skill are required of the observer for correct identification, and the results depend on the observer's capabilities.
In recent years, new types of effective pigments have been developed and marketed one after another. Of flaky metallic pigments, for example, more than 100 kinds of aluminum flake pigments have been marketed which vary in production process, coloring technique, and particle size grade, and examples of metallic pigments include aluminum flakes whose surfaces are coated with an organic pigment, aluminum flakes whose surface have iron oxide deposited thereon by CVD, aluminum flakes produced by vapor deposition, aluminum flakes which have so-called silver dollar-type smooth surfaces, etc. Further, there are more than 300 kinds of effective pigments other than aluminum flakes. Therefore, it is almost impossible for the observer to memorize the characteristics of all the effective pigments.
In Patent Document 1, only the particle diameter and coloring characteristics of effective pigments are used as characteristic parameters. Therefore, although the method disclosed therein can crudely assess the type of effective pigment used, it cannot specify the brand of the effective pigment.